While information content to be processed in a unit time has exponentially increased along with an explosive development in the information society, a dramatic decrease in energy made available for use in information-processing has been in strong demand from the standpoint of the global environment, and energy constraints. With a semiconductor operation element based on a CMOS, available up to now, performance has increased along with miniaturization, however, an increase in power consumption, induced by an increase in leakage current loss increasing due to the miniaturization, and AC loss together with joule loss, occurring when current flows through an interconnection, has become pronounced, so that it has become difficult to enhance a working speed. In order to cope with this situation, countermeasures have been taken for turning a block power off without using multi-cores whereby a plurality of processors are disposed, power gating, and so forth. It is deemed, however, that there is a limitation to any of the countermeasures.
Attention has lately been focused on a spin flow for transmitting information by means of a flow of spin without being accompanied by current flow, as a technology for realizing lower power consumption. Two types of spin flows exist in the spin flow, including an electron spin flow in which an electron propagating on a Fermi surface is a carrier, as described in, for example, Non-patent Document 1 {Nature, Vol. 416, pp. 713-715 (2002)}, and a spin-wave spin flow in which precession of spin constrained by a atom propagates in a ferromagnetic waveguide. The spin wave among them is relatively long, being in a range of several tens of μm to several cm, so that application of the spin wave to an operation circuit large in scale is hoped for.
There have been disclosed a method for effectively generating a spin wave, and a method for controlling a phase of a spin wave in, for example, in Japanese Unexamined Patent Application Publication No. 2009-508353, and further, an information-processing device making use of the fluctuating nature of reflection, refraction, transmission, interference, and so forth of a spin wave has also been disclosed therein. Further, in Non-patent Document 2 {IEEE TRANSACTIONS ON MAGNETICS, VOL. 44, NO. 9, pp. 2141-2150 (2008)}, there have been disclosed specific logic operation circuits using a spin wave (an AND circuit, an OR circuit, a NAND, a NOR circuit, and so forth) in addition to a method for exciting a spin wave, a method for detecting a spin wave, and a method for controlling a spin wave phase, thereby pointing to significant reduction in power consumption.
Still further, in Non-patent Document 3 {JOURNAL OF APPLIED PHYSICS, VOL. 110, p. 034306 (2011)}, there have been disclosed a spin wave operation circuit compatible with a present-day synchronous operation circuit where write-information is computed by use of a spin wave to be subsequently stored, thereby proceeding with the next information-processing. The content of the information-processing is briefly described hereinafter.
FIG. 1 is a view schematically showing the spin wave operation circuit disclosed in the Non-patent Document 3. Reference numeral 101 denotes an Si substrate, 102 a spin-wave waveguide wire-like (linear) in shape, 103 a ferromagnetic film made of Ni, and so forth, having an easy axis of magnetization in the longitudinal direction thereof, 104 a ferroelectric film made of PTZ, and so forth, 105 a metal electrode material film, made of Al, and so forth, and 106 a line of a metal material made of Al, and so forth. Reference numeral 107 denotes a region for exciting a spin wave, and 108 a detection region for detecting a spin wave. In this circuit, an operation using the spin wave is executed as follows. 103, 104, and 105 each indicate a magnetoelectric (ME) effect element capable of controlling the magnetic anisotropy direction of the ferromagnetic film 103 upon application of an electric field.
Further, description is given hereinafter with reference to an xyz coordinate system shown in FIG. 1. With the present invention, a direction vertical to a film surface is a z-axis direction, and a direction parallel with the film surface is a direction within an x-y plane.
Upon application of the electric field +, or − (More specifically, upward, or downward in the perpendicular direction) to the element, information “0”, or “1” is written to the ferromagnetic film 103. Next, an electric field identical in polarity to the +, or − electric field is applied to excite a spin wave. While the spin wave propagates through the waveguide to reach the Ni film in the lower part of the electrode line 106, a first operation is executed by making use of the fluctuating nature of the spin wave, and the result thereof is recorded in the Ni film. Next, while the electrode line 106 is activated to cause a spin wave to be excited again, and the spin wave propagates through the waveguide to reach the detection region 108, a second operation is executed by making use of the fluctuating nature of the spin wave, and the result thereof is recorded in the Ni film present in the region 108. The result of the operation is electrically detected via the ME effect elements present in the region 108.
FIGS. 2A to 2C each are a view showing the spin-wave waveguide 102, and the ME effect element in greater detail. In the spin-wave waveguide, magnetization of a ferromagnetic material is oriented in the perpendicular direction, as shown in FIG. 2B. In contrast, the Ni film 103 has the easy axis of magnetization in the longitudinal direction thereof, however, because the Ni film is magnetically coupled to a ferromagnetic film 102 of perpendicular magnetization, a magnetization direction thereof is unable to be oriented fully in the longitudinal direction, the magnetization direction is therefore oriented in a direction between the perpendicular/the longitudinal, as shown in FIG. 2C. Since one stabilization point exists in the respective directions of +y/−y, the information “0”, or “1” can be written to the Ni film.